He dislikes immigration on national security grounds (Mexico wants "La Reconquista" of the Southwest U.S., p.105)

...And just about every other grounds you can think of. Buchanan cites John F. Kennedy frequently -- demonstrating how JFK would be considered anti-immigrant today -- and also several times cites Kennedy's book, A Nation of Immigrants. But Kennedy's book was strongly pro-immigrant, even by today's standards, if one doesn't parse out just a few excerpts. But Buchanan's book might be considered the conservative response to JFK's book.

Buchanan verbalizes what the Tea Party currently says, and provides data for the anti-immigrant movement today. Buchanan is pretty extreme in his anti-immigrant attitude -- some might say so extreme as to be anti-Muslim and racist -- but lays out the basis of all of the anti-immigrant attitudes in today's politics.